/*
 * Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
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 *
 *
 *
 *
 *
 */

package com.sun.imageio.plugins.common;

import java.io.IOException;
import javax.imageio.stream.ImageOutputStream;

/*
 * Came from GIFEncoder initially.
 * Modified - to allow for output compressed data without the block counts
 * which breakup the compressed data stream for GIF.
 */
public class BitFile {

  ImageOutputStream output;
  byte buffer[];
  int index;
  int bitsLeft; // bits left at current index that are avail.

  /**
   * note this also indicates gif format BITFile.
   **/
  boolean blocks = false;

  /*
   * @param output destination for output data
   * @param blocks GIF LZW requires block counts for output data
   */
  public BitFile(ImageOutputStream output, boolean blocks) {
    this.output = output;
    this.blocks = blocks;
    buffer = new byte[256];
    index = 0;
    bitsLeft = 8;
  }

  public void flush() throws IOException {
    int numBytes = index + (bitsLeft == 8 ? 0 : 1);
    if (numBytes > 0) {
      if (blocks) {
        output.write(numBytes);
      }
      output.write(buffer, 0, numBytes);
      buffer[0] = 0;
      index = 0;
      bitsLeft = 8;
    }
  }

  public void writeBits(int bits, int numbits) throws IOException {
    int bitsWritten = 0;
    int numBytes = 255;  // gif block count
    do {
      // This handles the GIF block count stuff
      if ((index == 254 && bitsLeft == 0) || index > 254) {
        if (blocks) {
          output.write(numBytes);
        }

        output.write(buffer, 0, numBytes);

        buffer[0] = 0;
        index = 0;
        bitsLeft = 8;
      }

      if (numbits <= bitsLeft) { // bits contents fit in current index byte
        if (blocks) { // GIF
          buffer[index] |= (bits & ((1 << numbits) - 1)) << (8 - bitsLeft);
          bitsWritten += numbits;
          bitsLeft -= numbits;
          numbits = 0;
        } else {
          buffer[index] |= (bits & ((1 << numbits) - 1)) << (bitsLeft - numbits);
          bitsWritten += numbits;
          bitsLeft -= numbits;
          numbits = 0;
        }
      } else { // bits overflow from current byte to next.
        if (blocks) { // GIF
          // if bits  > space left in current byte then the lowest order bits
          // of code are taken and put in current byte and rest put in next.
          buffer[index] |= (bits & ((1 << bitsLeft) - 1)) << (8 - bitsLeft);
          bitsWritten += bitsLeft;
          bits >>= bitsLeft;
          numbits -= bitsLeft;
          buffer[++index] = 0;
          bitsLeft = 8;
        } else {
          // if bits  > space left in current byte then the highest order bits
          // of code are taken and put in current byte and rest put in next.
          // at highest order bit location !!
          int topbits = (bits >>> (numbits - bitsLeft)) & ((1 << bitsLeft) - 1);
          buffer[index] |= topbits;
          numbits -= bitsLeft;  // ok this many bits gone off the top
          bitsWritten += bitsLeft;
          buffer[++index] = 0;  // next index
          bitsLeft = 8;
        }
      }
    } while (numbits != 0);
  }
}
